Inhibitory Effect Of Polyphenols On The Formation Of Off-odors In Heated-treated Muskmelon Juice

Muskmelon is a extremely thermal-sensitive fruit,and could produce undesirable“cooking pumpkin” and “sulfurous” off-notes when processing temperature over 58oC,severely restricting the development of muskmelon deep processing industry.It has been reported that the addition of polyphenols can inhibit the off-notes of heat-treated milk and soybean milk,but the inhibition effect of polyphenols on thermally-produced off-odors in juice is rarely reported.In this paper,non-climacteric Honey Kiss muskmelon(NCM)and climacteric No.11 muskmelon(CM)were slected to study the cultivar differences in thermal-sensitivity of aroma profile.Then,the key off-notes were identified using the more thermal-sensitive melon cultivar as material.Lastly,the inhibitory effects of different kinds of polyphenols on off-notes were studied,and the mechanism of inhibition was preliminarily explored and analyzed.The main results are as follows:1.Differences in sensitivity to thermal processing of aroma profilies of two thick-skinnedmuskmelon cultivarsTo study cultivar difference in the aroma sensitivity to thermal processing,heat-induced aroma alterations of two muskmelon cultivars with different aroma profiles and postharvest physiologies were comparatively studied by combined use of qualitative descriptive analysis.Higher intensities of “fermented” and “sulfurous” off-notes and more drastic changes of volatile fingerprint were observed in non-climacteric Honey Kiss muskmelon juice(NCMJ)than those in climacteric No.11(CMJ).However,less agreeable odors and more offensive off-odors with higher MF values were identified in heated NCMJ than in heated CMJ.Both sensory and instrumental analysis indicated a cultivar difference in thermal-sensitivity of muskmelon aroma profile,and revealed a better original fresh notes-retaining and off-odors-inhibiting ability of CMJ than that of NCMJ.2.Identification of volatile off-flavors in heat-treated muskmelon juicePredominant contributors to thermally-induced off-notes in muskmelon juice(MJ)were investigated by combination of sensory evaluation,GC–olfactometry(GC–O),multidimensional GC and addition experiments.“Fermented” and “sulfurous” were the dominant heat-induced offensive off-notes,and fundamental heat-led changes in odorants were observed.Comparative aroma extract dilution analysis revealed that the off-flavors were mainly caused by newly heat-formed compounds.These included volatile sulfurs with “rotten” odors,Strecker aldehydes having “fermented” notes,and heterocyclics exhibiting “roasted” smells.Specifically,dimethyl sulfide,methional,methanethiol,dimethyl trisulfide,dimethyl disulfide,3-(Methythio)-1-propanal and acetaldehyde were the predominant off-note contributors.3.Study on inhibition effect of polyphenols on key volatile off-flavorsBy means of sensory evaluation combined with multiple comparison statistical method,the effects of different polyphenols on off-odors of muskmelon juice before and after different polyphenols were analyzed and quantitatively by headspace solid-phase microextraction combined with gas chromatography-mass spectrometry.Catechins,genistein,daidzein,phlorotannins and pyrogallol were found to have different inhibitory effects on off-note contributors in heat-treated muskmelon juice.4.Preliminary study on inhibition mechanism of catechin on 3-methylthiopropanalDuring the investigation on the inhibition mechanism of catechin on 3-(methythio)-1-propanal generation,it was found that the addition of catechin could effectively inhibit the methionine and glucose Maillard reaction pathway.Moreover,it was revealed using model system that addition of catechin couldreduce the partition coefficient 3-(methythio)-1-propanal and therefore decrease its release.